1. Field of the Invention
This invention relates to memory for computers and digital systems, and more particularly, dynamic random access memory (DRAM).
2. Description of the Related Art
To meet ever-increasing performance demands, the amount and density of memory in computer systems is continually increasing along with the demand for faster processors and other performance-enhancing advancements. As a result of the increasing memory demands, power consumption by memory subsystems has increased correspondingly. Increased power consumption has led to increased heat generation by memory subsystems, and thus leads to memory devices operating at a higher temperature.
The higher temperature at which some memory devices are required to operate may impact their performance and reliability. In particular, higher temperatures may impact the data reliability of dynamic random access memory (DRAM) devices. Information is stored in a DRAM in individual cells, which are essentially capacitors, storing information as an electrical charge. DRAM cells typically encounter what is known as leakage current, which causes the amount of electrical charge stored in the cell to decrease. If the amount of charge decreases enough, information stored in the cell may be compromised. Memory subsystems utilizing DRAM devices periodically provide a refresh cycle to restore the charge in the individual DRAM cells. However, higher operating temperatures tend to increase the amount of leakage current, and therefore the rate at which memory cells lose their charge. If the temperature is high enough, the periodic refresh cycles may be unable to ensure data integrity in the DRAM devices.
One method to counter the problems resulting from higher operating temperatures is to throttle memory access. A memory controller may limit access to DRAM memory devices when the temperature has exceeded a certain threshold. However, this may significantly reduce memory bandwidth, since the amount of time required for the DRAM devices to cool to a temperature below the threshold may consume a large number of memory cycles. This reduction of memory bandwidth can have a severe impact on computer system performance.